Nate Silver has a valuable rundown on the record of interim appointed US Senators. A data summary:
* 13 of the 49 (27%) ran for office, but were defeated in the general election;
* 7 of the 49 (14%) ran for office, but were defeated in the primary;
* 10 of the 49 (20%) chose not to seek a permanent term (including one who was prohibited by state law from doing so).
(It occurs to me that the parenthetical case there actually did not choose not to run.)
From that record, including some of the specific cases discussed by Nate, it seems clear that the poor reelection record of these interim Senators would be expected from the common practice of Governors choosing objectively weak candidates. Apparently, many of them have had no prior electoral experience or other record of achievement. Of course, that may be deliberate, either as deference to the party or electorate or as a simple short-term patronage exchange (with the current Illinois scandal being an extreme case of the latter).
Nate also notes the institutional variation among states in filling vacancies:
states can move to solve the problem themselves by passing a “fast” special elections law, as states like Oregon, Wisconsin and Massachusetts now have (and Illinois soon will). Other states have evolved other checks and balances; Utah and Wyoming require that the candidate be selected from among a list prepared by the state party apparatus, while Alaska, Hawaii and Arizona require appointees to be from the same party as the departing senator. Arkansas provides for gubernatorial appointments, but does not allow the appointee to run for re-election.
Clearly, the process of gubernatorial appointment* needs reform. But it is clear to me that the answer is not what one commenter suggests: that every elected official should have a “vice” (meaning a stand-by replacement, not the other meaning it might more accurately imply!). Many Latin American countries have such a suplente system, and it is much abused–a cure worse than the disease.
* Something that is not clear to me is whether Illinois or any other state allows for outright appointment by the Governor, or if the actual process is nomination by the Governor, followed by appointment upon conformation by the state legislature. It is my recollection that California, at least, has an “advise and consent” provision. The media coverage on Illinois leaves the impression that the Governor chooses unilaterally. I do not know if that is so. Maybe politically it does not matter in the current Illinois case: anyone with appointment–even if confirmed by elected representatives of the state’s electorate–would be branded, rightly or wrongly, as Blagojevich’s man or woman. But it certainly means that a wounded governor would have to defer to a representative body’s preference.